This invention relates to tape measures, and more particularly, to a coiled measuring tape adapted to be locked in an extended or unwound position.
Length-measuring instruments including coiled tapes, made of steel or like material, are well-known. In such devices, the measuring tape is coiled about a spool in a housing by means of a recoil spring and the drawing of the tape from the housing acts against the action of the recoil spring. Such devices are shown, for example, in U.S. Pat. Nos. 3,318,550; 3,521,831; and 3,905,114.
In such devices, there is often provided a braking member which is adapted to retain the tape in an extended position when unwound to a desired measuring length. The utilization of a braking member eliminates the need for the user to grasp the tape to prevent it from being rewound by the recoil spring entirely into its casing. Although various types of braking devices have been proposed, one such device, to which the present invention is directed, includes a braking lever which is pivotally attached to the housing and has an end which is normally biased to engage the tape extending out of the housing opening, for example, as shown in U.S. Pat. Nos. 3,220,112 and 3,610,548.
Typically, in coilable rule tape measures, the free end of the coiled tape includes a hook portion which engages the housing when the tape is in its fully retracted position. In this manner, the tape is prevented from totally recoiling within the housing and the hook portion can be grasped during successive uses for unwinding the tape. However, the coil spring used to rewind the tape into the housing is very strong and imparts a tremendous shock to the hook portion when the tape is rewound in the housing, that is, when the hook portion hits against the housing. This shock tends to break the hook portion from the free end of the tape, resulting in the tape totally recoiling within the housing. Accordingly, shock absorbing members have been provided which absorb the shock when the hook portion hits against the housing. Such devices take various forms, such as a spring-loaded member, shown in U.S. Pat. No. 3,519,220, and a resilient stop extending from the housing against which the hook portion hits, shown in U.S. Pat. No. 3,578,259.
Another shock absorbing tape rule device, which provides a combination of both braking and shock absorbing, is shown in U.S. Pat. No. 4,153,996. That device includes a braking lever pivotally mounted to the housing by a pivot pin disposed in an elongated slot. The braking lever has a front end disposed adjacent the housing opening for engaging the tape. A coil spring at the other end of the braking lever biases that end away from the housing and is angularly disposed between the housing and braking lever so as to exert a vertical biasing force, which biases the front end about the pivot pin and towards the tape, and a longitudinal or horizontal biasing force, which biases the pivot pin towards the front end of the elongated slot. Thus, when the hook portion at the end of the tape hits against the front end of the lever, much of the impact is absorbed by the coil spring causing the pivot pin to travel towards the rear of the elongated slot until the coil spring recovers to return the pivot pin back to its original position. However, this device has certain disadvantages. For example, because the coil spring is not acting totally in the vertical direction, a lesser force is exerted in this direction, necessitating a larger coil spring. Further, because of the tremendous impact of the hook portion against the lever, there can be wear on the coil spring, eventually resulting in degradation of the coil spring and, consequently, of the braking action of the lever.